While the invention has other application, it is particularly well suited to the task of positioning and heating electronic components at the work stations of ultrasonic, wire bonding machines. The current universally accepted method of completing wire connections between circuit points in micro circuitry utilizes sonic energy applied to the wire at the point at which the wire overlies the circuit. The wires are formed of gold or aluminum. They are maleable and may be less than one mil in diameter, and, while the forces applied by the bonding tools are very small, the wire is easily damaged in the process of applying bonding energy. The problem of wire damage can be overcome in large measure by heating the circuit point to which the wire is to be bonded. Heating facilitates bonding so that it is accomplished in less time and with less force. That is true especially in the case of gold wire and gold plated circuits, and it is common practice to heat the circuit to temperatures in the range of 300-500 degrees centrigrade. At 500 degrees centrigrade, steel color changes to light straw. Many materials that could otherwise be employed in work place construction cannot withstand such temperatures. Materials that can be used may undergo significant degrees of expansion.
Once the workpiece is positioned in a predefined initial position under the bonding tool, and its rotational orientation is correct, the tool may be controlled to execute a series of bonding and wire payout and severing events. The work holder is rotated to rotate the workpiece according to some predefined program. But whether the task is to be accomplished in such semi-automatic fashion or manually, the quality of the finished work is likely to depend upon the ability of the holder to ensure that its axis of rotation is not tilted or translated and to maintain the workpiece in the prescribed position. The circuit pads to which the wires are bonded may have an area comparable to the cross-sectional area of a human hair. In that circumstance, even minute dimensional changes in the work station present a major difficulty. The work station is necessarily large enough for manual manipulation. Its dimensions are several orders of magnitude greater than the dimensions of the circuit pads. Dimensional change and back lash, which is a very small percentage of work station size, can readily represent huge, intolerable changes when translated to the workpiece.
Heated work stations have been employed in the past, but prior stations were little more than the combination of a heater mounted in a portable stand and a clamp by which to hold a workpiece. The function of such stations was limited to holding the workpiece steady. All positioning was accomplished by positioning of the tool at each bonding point.